I had one of the handi rifles in 300BO and it was fun. The break actions suppress fine, I've also seen .38spl that was also stupid quiet.

As far as 45/70 I think you will be disappointed. I run a 458 SOCOM on 16" barrel with Hybrid suppressor. Was at the range last week showing friend with a lever 45/70 that it is rather loud, even with subs. Friend decided not to suppress his lever gun.

My 300BO had 16" barrel, but balance was very muzzle heavy with a Saker on the end. I think a CVA with 22-25" barrel would be way worse.

My 458 SOCOM is sweet can or not so no regrets. But if I were going single shot I'd go .357, .44mag or .460S&W for the option of .38spl, .44spl and 45 Colt.